1. Field of the Invention
This invention relates to sensors of the type that can be adhered to an article to be monitored and which change state as an incident of being removed from the article.
2. Background Art
For decades, purveyors of articles who display the articles for consumer inspection have sought effective systems for preventing unauthorized removal of these articles from the display area. Designers of these types of systems have contended with many objectives which are often competing with each other. Most significantly, it is important that the system effectively deter theft. Cost is always a significant consideration in the design of such systems. It is also important that the systems be user friendly, i.e., that they can be easily and consistently activated. The more complicated the systems become to operate, the more likely it is that employees will improperly set the systems up or altogether avoid activation thereof. At the same time, it is desirable that these systems be relatively unobtrusive. Large, electronic sensors on a relatively small article may detract from the visual appeal to the potential consumer. On a small article, a relatively large profile sensor may also inhibit effective inspection of the article.
One sensor design that meets a number of the above objectives is that which uses a flexible substrate as the main body of the sensor. A conductive trace is provided on the substrate, with an adhesive applied to the substrate to facilitate adherence of the sensor to an article to be monitored. The tenacity and the location of the adhesive may be selected to cause part of the conductive trace to remain on the substrate and part on the article as the substrate is peeled away from an article to which it is adhered. The sensor is electrically connected to a monitoring system which produces a detectable signal as an incident of detecting that the conductive path defined by the trace has been interrupted.
One version of this sensor applies adhesive at only selected locations on the substrate and over the trace. When the substrate is peeled off, the adhesive is designed to maintain a part of the trace bonded to the article. The unbonded portion of the trace separates with the substrate to cause interruption of the conductive path defined by the trace.
It is also known to cause part of the trace to be bonded more securely to the substrate than with the adhesive layer over part thereof, and another part to be more securely held to the adhesive layer than to the substrate. This produces the same effect upon the substrate being peeled from the article to which the sensor is attached.
In both of the above versions, the substrate is designed to remain substantially intact as the substrate is peeled from the article that is monitored.